1. Technical Field
The present disclosure generally relates to the field of radio-frequency signal receivers. More particularly, the present disclosure relates to an electronic device with an automatic gain control for receiving radio-frequency signals, for example GPS (Global Positioning and navigation System).
2. Description of the Related Art
A radio-frequency signal receiver comprises an amplifier of the received radio-frequency signal and an analog-to-digital converter for converting the amplified radio-frequency signal into a digital signal.
The received radio-frequency signal comprises both the useful signal and noise. One of the most important noise contributions is that of high-power interference signals which can have a bandwidth which overlaps (at least partially) the bandwidth of the useful radio-frequency signal or of the high-power interference signals, which do not have a bandwidth overlapping the useful signal bandwidth, but that can cause a noise when non-linear effects are present in the radio-frequency signal receiver. For example, the useful signal is GPS and the interference signal is a radio-mobile signal including GSM (Global System for Mobile communication), EDGE (Enhanced Data rates for GSM Evolution), CDMA (Code Division Multiple Access) or WLAN (Wireless Local Area Network)-type.
The interference signal can have a high power and thus the received radio-frequency signal can assume values within a wide range; as a result, also the radio-frequency signal in input to the analog-to-digital converter can assume values within a wide range and the analog-to-digital converter can saturate.
Therefore it is typical to use an amplifier with an automatic gain control and to reduce the amplifier gain in order to decrease the value of the input signal to the analog-to-digital converter and to keep the values of the signal in input to the analog-to-digital converter within a determined range wherein the analog-to-digital converter works correctly, thereby preventing the analog-to-digital converter from saturating and also ensuring an efficient use of the dynamic range.
A known prior art to carry out the automatic control of the amplifier gain is as described in the US Patent Application USA having publication number US 2005/0031057-A1, wherein it is disclosed that the amplifier gain is controlled by means of the measure of the output power from the analog-to-digital converter estimated with the measure of the bit switching rate of the output signal from the analog-to-digital converter, within a determined time interval.
However, since the received radio-frequency useful signal received (for example, GPS) can be very weak, the reduction of the amplifier gain (caused by a high power interference signal, as explained above) also reduces excessively the power of the useful radio-frequency signal and thus the information carried by the useful radio-frequency signal cannot be detected correctly due to a high bit error rate.
A prior art for solving the problem of high-power interference signals in the radio-frequency signal is to detect, in the base-band module, the presence of the high-power interference signal and not to take into account the signal received from the radio-frequency module, which remains active, thereby dissipating power uselessly.
Another prior art is to detect in the base-band module the presence of the high-power interference signal and to switch off one or more blocks of the radio-frequency module (for example, the amplifier or the analog-to-digital converter). This prior art has the disadvantage that it requires to check periodically the presence of the high-power interference signal for reactivating the blocks of the radio-frequency module.
Both prior arts have the disadvantage of having, when the high-power interference signal arrives, an excessively too long time interval, wherein the base-band module processes erroneous samples.
The applicant has noticed that the prior arts have at least one of the following disadvantages:
they require too much time to detect the presence of high-power interference signals;
they may require too complex dedicated resources;
they may require the transmission of additional information from the radio-frequency module to the base-band module for the base-band detection of the presence of high-power interference signals;
they transmit unnecessarily erroneous bits from the radio-frequency module to the base-band module.